This invention relates to a test circuit for monitoring systems, and particularly for testing the operation of the system in response to a demand signal.
In various operating systems, the various components in the systems are monitored to detect the status of the system and also to locate a failure of a component, or a fault in the system operation. For example, the co-pending application of John J. Deisinger et al, entitled "Water Heater Diagnostic Apparatus" filed on Oct. 16, 1987 with Ser. No. 07/109,707 discloses a diagnostic system for monitoring a commercial hot water heater unit wherein the several components of the system are separately monitored and a signal coupled into a unique detection system for monitoring the state of the system components and the system functions. For example, in a gas fired hot water heater, the diagnostic system monitors the state of the main burner unit and the pilot burner unit for igniting the main burner. An indication may also be incorporated into the system to indicate various burn levels through corresponding monitoring of the state of the several control valves. The above Deisinger et al patent application discloses a particularly satisfactory diagnostic system with a unique coupling of the sensed signals into a display circuit including individual LED lamps for each component or function being monitored. Experience with the system has indicated that under certain fault conditions with respect to the burning system, a fault condition may be detected. The fault may occur in various stages or components but the specific fault source is not readily determined. A burner fault may for example result from a failure of one of the automatic sensors, the automated actuators or a manually set valve. If the manual gas valve is not opened, the system will indicate a fault condition with the illumination of the associated burner status lamp. Similarly, if a gas flow valve should malfunction, a similar fault condition will be indicated. Although diagnostic systems thus allow monitoring basic fault areas as well as particular parts, the necessity to check the various points of possible error may require an undesirable time with an attendant, cost and annoyance factor.
British patent No. 2,082,360, for example, discloses a monitoring system having a pair of LEDs, one for the pilot valve and one for the burner valve. A special interconnecting circuit is provided to indicate burner shut down with special interlocking switches such that the power is removed from the other indicating circuit once a lamp is illuminated to pin point a fault position. The system provides for an indication of burner failure either during start up or during normal operation with a similar indication provided. Such circuit requires a plurality of the interlocking switches with interlocking circuitry between the several monitoring circuits for particular switches and components.
Although such systems have been suggested, there is a need for a simple, reliable and effective monitoring circuit which will separately signal that the failure has occured during a start up condition. The service personnel can then directly monitor the several elements involved in such a failure which may be as simple as the failure to open the manually controlled valve for supplying of gas to the burner system including both the pilot valve and the main burner valve. There is in summary a need for a specific source identification of a failure within a sequentially actuated system such as the burner control for a hot water heating unit or the like without increasing the complexity of the system unduly.